The present invention relates to a method of increasing the pressure or raising the enthalpy of a fluid flowing at supersonic speed, wherein vapor is mixed with liquid, and this mixture is accelerated to supersonic speed after which a condensation shock is triggered.
First, the fundamental problem of flowing mixtures of two-phase mixtures, for example air/water or vapor liquid, or the like, should be addressed.
In such mixtures, the xe2x80x9csonic speedxe2x80x9d may have small values, whereby xe2x80x9csonic speedxe2x80x9d is understood as the value that is decisive for the formation of the Mach number (See VDI-Zeitung (VDI-Journal) 99, 1957, No. 30, 21. October, xe2x80x9cxc3x9cberschallstrxc3x6mungen von Hoher Machzahl bei kleinen Strxc3x6mungsgeschwindigkeitenxe2x80x9d (Supersonic Flows of High Mach Number at Low Flow Speeds) by Carl Pfleiderer, pp. 1535 and 1536; and xe2x80x9cGrundlagen Fxc3xcr Pumpenxe2x80x9d (Basics for Pumps) by em. Prof. Dipl.lng. W. Pohlentz, VEB Publishers Technik, Berlin 1975, pp. 49 and 41).
Likewise, Ostwatitsch points out, that in frothing flows at xe2x80x9csupersonic speedxe2x80x9d all phenomena occur as known from single-phase supersonic flow (see xe2x80x9cGasdynamikxe2x80x9d (Gas Dynamics), Dr. Klaus Ostwatitsch, Vienna, Springer press 1952, page 440). The analogy between two-phase flow and single-phase flow of a compressible fluid is total. Thus, a convergent-divergent nozzle (Laval nozzle) is thus also needed for acceleration of a two-phase flow from xe2x80x9csubsonic speedxe2x80x9d to xe2x80x9csupersonic speedxe2x80x9d, and the opposite process is possible only by means of a compression shock, or a series of compression shocks. The processes in the compression shock in the two-phase flow are likewise exceedingly complex, whereby it is surprising that the relationship between shock entry speed and shock exit speed as well as the rise in pressure is established by the flow of heat. (See xe2x80x9cTechnische Fluidmechanikxe2x80x9d (Technical Fluid Mechanics) by Herbert Sieglach, VDI publishers 1982, pp. 214-230, and W. Albring, xe2x80x9cAngewandte Stxc3x6mungslehrexe2x80x9d (Applied Flow Instructions), 4th Edition, publishers Theodor Steinkopff, Dresden, 1970, pp. 183-194). The shock intensity is determined by the size of heat quantity which flows in the shock from subsonic to supersonic.
Furthermore, compressible two-phase flows behave such that the state variablesxe2x80x94with the exception of the entropy, the temperature and the rest temperaturexe2x80x94change in opposite direction in the subsonic and supersonic range. (See E. Truckenbrodt, xe2x80x9cFluidmechanikxe2x80x9d (Fluid Mechanics), Volume 2, Springer Verlag 1980, page 68). For example, supply of heat to a supersonic flow means a delay, whereas supply of heat to a subsonic flow means an acceleration.
The strength of the so-called condensation shock is dependent on the amount of condensing water vapor (see Dr. Klaus Oswatitsch: Gasdynamik, Springer Verlag 1952, page 57).
The condensation shock is generated during flow of a fluid which contains oversaturated water vapor and is the result of a sudden condensation of the vapor which occurs very rapidly and within a narrow zone, designated xe2x80x9ccondensation shock areaxe2x80x9d. The stability of the condensation shock in relation to small perturbances in the direction vertical to its area, depends on the thermodynamic condition of the vapor prior to the shock which should just about coincide with the start of the rapid condensation of the vapor. A detailed derivation of this process is found in L. D. Landau and E. M. Lifschitz: Hydrodynamik (Hydrodynamics) Academy-Verlag, Berlin 1966.
The mechanism of pressure rise is grounded in the fact that condensation of the vapor generates vacuum spaces which suddenly fill up with incoming fluid at sonic speed. The thus resultant kinetic energy is then transformed into pressure.
The extent of the pressure increase as a result of condensation is dependent on the temperature difference between the vapor and the fluid, or on the fluid temperature during mixture with vapor and on the location of the compression shock.
In tests conducted with water and water vapor, a pressure was registered, after complete condensation, via the compression shock, which pressure is sufficiently great to utilize the apparatus as a feed pump.
According to a conventional design of the above-mentioned type, known, for example, from EP 0 555 498 A1, liquid is withdrawn prior to the placement of the condensation shock in order to assure that the condensation shock takes place in the designated range. Furthermore, it is realized in the known design that the liquid, continuing to flow in the diffuser, is not excessively heated.
In accordance with the subject matter of the invention, additional liquid is introduced, before the condensation shock is triggered, in the mixture which flows at supersonic speed. As a result, the pressure in the condensation shock further increases since the higher liquid content contains a higher flow energy in the vapor/liquid mixture.
Advantageously, the supply of the additional liquid can be effected through the underpressure generated by the flowing mixture, thereby rendering the need for additional means for conveying the added liquid unnecessary.
An advantageous apparatus for carrying out the process according to the invention, includes a vapor acceleration nozzle, a feed slot for a liquid medium, a converging mixing nozzle, and a diffuser, with a parallel flow section being provided between the mixing nozzle and the diffuser and including a slot which divides the parallel flow section and has a length which, measured in the direction of the flow, is about 0.5 to 0.9 times the diameter of the parallel flow section. Through this slot size, a sufficient amount of additional fluid can be drawn in automatically, without impairing the flow of the vapor/liquid mixture.